Survey and construction activities necessarily involve measurement of distances and/or angles, for placement of new marks or for location of marks already set down. One conventional method of performing such measurements is by use of a transit and pole, theodolite, or electronic distance measuring equipment (EDM). This requires use of cumbersome equipment, usually by at least two persons, for example, one operating the transit and the other holding the pole. If measurements are being made sequentially, an error in one distance or angle measurement will often be incorporated in all later measurements in that sequence. Workers in this field have developed other approaches that do not rely upon use of a transit and pole, theodolite or EDM for survey purposes.
A geodetic survey system using a digital phase meter is disclosed by Jaffe in U.S. Pat. No. 3,522,992. The apparatus measures distances and changes therein between a transmitter and a receiver, by combining, modulating and transmitting two laser beams having different frequencies and measuring their corresponding phase difference at the receiver. The modulated composite light beam is split by a dichroic mirror, and the phase and intensity of each of the two frequency component signals (modulated) is analyzed to determine an initial or reference modulated waveform. The reference waveform is compared with a subsequently received waveform having the same signal frequency to determine any changes in the transmitter-to-receiver optical distance or in the refractive index of the intervening transmission medium. This apparatus requires transmission of two or more light beams along a line of sight, and the apparatus does not appear to be hand-held or transportable by one person.
Davidson et al, in U.S. Pat. No. 4,225,226, disclose use of a rotating laser beam transmitter/receiver to guide an aircraft or similar vehicle that overflies a field or region in a specified pattern for a particular purpose, such as crop spraying. The rotating laser beam transmitter/receiver, which is carried by the aircraft, produces a light beam that is reflected from a sequence of reflectors on the ground that are positioned at known locations relative to each other. The reflected return signals from the ground reflectors allow the aircraft to determine its present location and to fly in the specified pattern relative to these reflectors. It appears that the pattern must be determined and entered before the aircraft begins its work.
A similar approach is disclosed in U.S. Pat. No. 4,398,195, issued to Dano, using radar signals emitted from the aircraft and received and returned by three transponders, positioned at spaced apart locations surrounding the region over which the aircraft pattern is to be flown. The aircraft carries a radar trilateralization receiver that receives and analyzes the return radar signals.
A guidance system for an earth-working vehicle, such as a tractor, is disclosed in U.S. Pat. No. 4,244,123, issued to Lazure et al. A signal transmitter, such as a rotating laser beam source, is positioned in a field to be worked, and two signal receivers are positioned at fixed, spaced apart, longitudinal locations on the vehicle, to distinguish changes by the vehicle in two horizontal directions. The receivers determine and report on the present location and bearing of the vehicle, based on what may be a phase difference of the signals received at the two receivers.
A similar approach is disclosed by Goyet in U.S. Pat. No. 4,677,555, where a rotating laser beam defines a reference plane for the earthworking vehicle. Datum points, defined by several beacons fixed in the ground and indicating the pattern (bearing, elevation) to be followed by the vehicle, are provided. A microcomputer carried on the vehicle monitors the pattern followed by the vehicle.
U.S. Pat. No. 4,309,758, issued to Halsall et al, discloses an unmanned land vehicle guided by three omni-directional light detectors carried on the vehicle. At least two spaced apart light sources must be provided off the vehicle, with each detector receiving light from two of the light sources. The vehicle bearing and location appear to be determined by signal phase differences for light from a common source arriving at the different detectors.
Stephens discloses a guidance and control system for one or more land vehicles in U.S. Pat. No. 4,647,784. Each vehicle generates and transmits a light beam that is reflected from each of two or more reflectors, each reflector having its own optical code (for example, stripes having different light reflectivities) and being oriented to reflect and return the light beam to a light detector carried by the vehicle. The returned light beams from each beam are analyzed to determine the present bearing of the vehicle.
A method of automatically steering a land vehicle, such as a tractor, along a selected course in a field is disclosed in U.S. Pat. No. 4,700,301, issued to Dyke. A rotating laser beam source and directional light detector/processor are mounted on the vehicle, and two or more reflectors are positioned at or near the boundary of the field. The laser beam is reflected from the reflectors, returns toward the vehicle, and is received by the detector/processor, which determines the present location of the vehicle and its present bearing. In another alternative, two rotating laser beam sources are positioned near the edge of the field, the the laser beams emitted by these sources are received by an omni-directional light detector carried on the vehicle.
Use of a rotating laser beam for two-dimensional navigation of a land vehicle in a specified region is also disclosed by Boultinghouse et al in U.S. Pat. No. 4,796,198. Three or more reflectors, one having a distinctive reflectivity, are positioned near the boundary of the region to reflect the laser beam back to the vehicle, where the reflected beams are received by a photoelectric cell and generate signals with associated beam arrival directions that allow determination of the present location of the vehicle. Distinctive reflection from the one mirror provides an indication of the angular position of the laser beam on each rotation.
U.S. Pat. No. 4,807,131, issued to Clegg, discloses an automated land grading system in which the position of a cutting blade is controlled automatically to provide controlled shaping of a land region being graded. A laser beam is projected in a predetermined pattern across the land region, and a laser detector carried on the grading machine receives the beam and approximately determines the location of the cutting blade and the blade angle and depth appropriate for grading that location in the land region. Information on the desired blade angle and depth is stored by a microprocessor carried on the grading machine and is compared with the actual blade angle and depth to correct the blade orientation and elevation.
Olsen et al disclose survey apparatus for collection and processing of geophysical signals, using a Global Positioning System, a GPS base station and one or more data acquisition vehicles, in U.S. Pat. No. 4,814,711. Each vehicle carries geophysical measuring instruments, a GPS signal receiver and processor to determine present location, a visual display of present location, and radio communication equipment to transmit location information to the base station. The base station periodically polls and determines the present location of each vehicle, with reference to a selected survey course that a vehicle is to follow. The base station transmits commands to each vehicle to keep that vehicle on the selected course. Each vehicle also transmits results of the geophysical data it has measured to the base station for correlation and possible display at the base station. This apparatus requires continual tracking, control and correction of the course of each vehicle relative to the desired course and requires use of non-portable apparatus (a vehicle and its equipment) to provide the desired location and data measurements. All such measurements are transmitted to, and analyzed by the stationary base station, and the measurements probably are accurate only to within a few meters.
U.S. Pat. Nos. 4,870,422 and 5,014,066, issued to Counselman, disclose method and apparatus for measuring the length of a baseline vector between two survey marks on the Earth's surface, using a GPS signal antenna, receiver and processor located at each mark to determine the location of at mark (accurate to within a few meters). The location data are determined using GPS carrier phase measurements at each survey mark and are transmitted to a base station for analysis to determine the baseline vector length between the two marks. This approach requires use of two survey spaced apart survey marks and a base station. Use of GPS signals from five or more GPS satellites and use of a surveying time interval of length .DELTA.t.gtoreq.5000 seconds are required in order to reduce the mark location inaccuracies to a less than a centimeter.
Paramythioti et al, in U.S. Pat. No. 4,873,449, disclose method and apparatus for three-dimensional surveying, using triangulation and a laser beam that propagates along the perimeter of a triangle. A rotatable mirror, a component of the scene to be surveyed and a light-sensing camera are located at the three vertices of the triangle, and knowledge of the angles of orientation of the rotatable mirror and the camera allow determination of the location of the component of the scene presently being surveyed. Three spaced apart stations, including one station at the scene to be surveyed, and line-of-sight light beam receipt are required here.
Survey apparatus and method for mapping a portion of an ocean bottom are disclosed by Gaer in U.S. Pat. No. 4,924,448. Two ships, each equipped with identical GPS signal antennas, receivers and processors, move along two parallel routes a fixed distance apart on the surface of an ocean. Each ship takes radio soundings of a small region of the ocean bottom directly beneath itself and receives a reflected radio sound from that same region that is originally transmitted by the other ship. The depths of the region directly beneath each ship, as determined by each of the two radio sound waveforms and by the GPS-determined locations of the two ships, are determined and compared for purposes of calibration.
In U.S. Pat. No. 4,954,833, issued to Evans et al, a method for determining the location of a selected and fixed target or site, using a combination of GPS signals and the local direction of gravitational force. Geodetic azimuth is determined using GPS signals, and the local gravitational force vector is used to relate this location to an astronomical azimuth, using a fixed coordinate system that is independent of the local coordinate system. The target and a reference site are each provided with a GPS signal antenna, receiver and processor to determine the local geodetic azimuth.
A method for waste site characterization using GPS is disclosed by Reeser in U.S. Pat. No. 4,973,970. A GPS base station is established on the site, and a plurality of GPS roving receivers, each combined with a contamination level monitor, is used to determine locations of sites for core sampling. Experimental cores are formed in, and pulled from, the waste and examined for contamination level. The GPS-determined location of the core site is transmitted to the base station for archiving and any further hazardous material analysis.
Evans, in U.S. Pat. No. 5,030,957, discloses a method for simultaneously measuring orthometric and geometric heights of a site on the Earth's surface. Two or more leveling rods are held at fixed, spaced apart locations, with a known baseline vector between the rods. Each rod holds a GPS signal antenna, receiver and processor that determines a GPS location for each rod. The geometric height of the GPS antenna (or of the intersection of the rod with the Earth's surface) is determined for each rod, and the geometric height difference is determined, using standard GPS measurements (accurate to within a few meters). The orthometric height difference for each GPS antenna is determined using the measured GPS location of each rod and an ellipsoid or geoid that approximates the local shape of the Earth's surface.
A surveying instrument that uses GPS measurements for determining location of a terrestrial site that is not necessarily within a line-of-sight of the satellites is disclosed in U.S. Pat. No. 5,077,557 issued to Ingensand. The instrument uses a GPS signal antenna, receiver and processor combined with a conventional electro-optical or ultrasonic range finder and a local magnetic field vector sensor, at the surveyor's location. The range finder is used to determine the distance to a selected mark that is provided with a signal reflector to return a signal issued by the range finder to the range finder. The magnetic field vector sensor is apparently used to help determine the surveyor's location and to determine the angle of inclination from the surveyor's location to the selected mark.
U.S. Pat. No. 5,099,245, issued to Sagey, discloses a satellite-based location system for airborne vehicles, using a Geostar satellite system. Three or more ground base stations with known locations each receive a transmitted timing signal from a satellite. The base stations retransmit this signal with an identifying tag, after a pre-selected time delay, to the airborne vehicle. The times of retransmitted signal arrival are noted by the vehicle and are used to determine the vehicle's present location by triangulation.
A spatial position determining system using three or more (preferably four) fixed reference stations and a portable signal sensor is disclosed by Lundberg in U.S. Pat. No. 5,100,229. Each reference station is provided with a rotating laser beam source and a radiowave or light wave strobe transmitter that is triggered each time the corresponding rotating laser beam passes a specified angular position in its sweep. The portable signal sensor is positioned at an arbitrary location spaced apart from each of the strobe transmitters. When the sensor receives either the laser beam or the strobe pulse from each reference station, the time of receipt is entered in a computer connected to the sensor, and the sensor location is determined by the computer by triangulation.
Dornbusch et al, in U.S. Pat. No. 5,110,202, discloses use of a three-dimensional positioning and measurement system that uses three or more fixed base stations, each having a rotating laser beam, and one or more portable and movable stations, each having a laser beam detector, a computer and a visual display. As each laser beam rotates one revolution about an approximately vertical axis, this produces an electrical pulse at the detector, which pulse is time stamped by the computer. Knowledge of the time associated with appearance of the laser-generated pulse for contemporaneous revolutions for the base station lasers allows determination of the position of the portable station. An alternative approach uses two counter-rotating laser beams at each of two fixed base stations.
A satellite-based ground location determination system using two geostationary satellites and a fixed ground base station is disclosed by Toriyama in U.S. Pat. No. 5,111,209. A mobile vehicle whose location is to be determined transmits an initial signal through one of the two satellites to the base station, and the base station transmits a return signal through each of the two satellites to the mobile vehicle. The vehicle location is then determined by some form of triangulation. It is unclear how ambiguities in location can be removed using only two satellites.
U.S. Pat. No. 5,144,317, issued to Duddek et al, discloses use of a fixed GPS base station and four or more GPS satellites to monitor progress in an open pit mine, including determination of the location and spatial orientation of selected mining equipment, such as a bucket wheel of a travelling excavator. A second GPS receiver is positioned on the equipment item to help determine orientation and movement of the equipment.
A geodetic surveying system using three or more non-collinear GPS base stations and a roving land vehicle carrying a fourth GPS receiver is disclosed by Spradley et al in U.S. Pat. No. 5,155,490. The location of each GPS base station must be initially determined over a long period of time (10-12 hours). The land vehicle also carries a GPS receiver and receives GPS signals from four or more GPS satellites and from each base station. Vehicle location data determined from these signals appear to be post-processed to determine the vehicle's location at some time in the past.
These approaches rely upon measurements made using one or more laser beam or similar means, use cumbersome equipment, rely upon line-of-sight measurements, employ two or more persons for operation, and/or do not provide the accuracy required for many survey and construction activities. What is needed is an approach that (1) allows use of handheld devices for mark location, (2) allows location in real time of a new mark that is initially identified only in a database, (3) does not require two or more persons to implement the approach, (4) does not require line-of-sight measurements between two survey equipment items, (5) provides distance measurements and angle measurements, for mark location and generation purposes, accurate to within a few centimeters and to within a fraction of a degree, respectively, and (6) allows use of a single base station as a reference for measurements.